Atherosclerosis is considered an inflammatory disease triggered by the entry of monocytes into the wall of large arteries, where they differentiate into macrophages and foam cells and promote growth and dedifferentiation of smooth muscle cells. Several adhesion molecules on endothelial cells, monocytes and platelets are relevant for the binding of monocytes. In order to investigate the molecular mechanisms of monocyte recruitment to atherosclerotic lesions, we have recently developed an ex vivo model in which monocytes or monocyte-like cell lines are perfused through carotid arteries isolated from apoE-/-mice, and their interaction with the vessel wall is investigated by intravital microscopy. Monocyte adhesion under flow depends on activation of integrins, which we hypothesize to be initiated by chemokines presented on the endothelial surface at lesion-prone sites. We recently found that platelets can also interact with the atherosclerotic endothelium in the carotid artery of apoE-/-, but not control mice. The overall hypothesis of this project is that specific chemokines expressed on atherosclerosis-prone endothelium trigger monocyte and platelet arrest through binding of integrins to their ligands. We propose to (1) measure the expression of adhesion molecules, chemokines, and chemokine receptors in apoE-/- mice by immunostaining and flow cytometry; (2) investigate the mechanisms by which monocytes roll, adhere and become activated at lesion-prone sites in arteries of apoE-/- mice by using our isolated-perfused carotid artery and response-to-injury models; (3) investigate the molecular mechanisms by which platelets roll and adhere at lesion-prone sites of the mouse carotid artery, and on established lesions; and (4) test the impact of inhibiting, eliminating or blocking adhesion molecules, chemokines and chemokine receptors identified in specified in specific aims 1, 2 and 3 on accelerated lesion development in apoE-/- mice undergoing controlled vascular injury by histology and MRI. We have already identified P-selectin, VCAM-1, PSGL-1 and VLA-4 as key adhesion molecules. We will now determine the roles of ICAM-1, CD18 integrins and selectin ligands. We focus on chemokines presented by the atherosclerotic endothelium that can arrest rolling monocytes or platelets, and their receptors on these cells. These studies are designed to (1) provide insight into the molecular mechanisms of monocyte and platelet recruitment to atherosclerotic lesions and (2) test their relevance in an established model of arterial injury in apoE-/- mice.